1. Field of the Invention
The invention relates to the field of analog circuit design and in particular relates to the design of cascaded amplifiers wherein temperature independence and accurate gain control is provided.
2. Description of Related Art
In certain types of applications accurate cain control in portions of the electronic circuitry is essential to the effective or useful functioning of the system. One such class of systems include radar systems, particularly those radar systems which require multiple channels and accurate equal gain control.
In the prior art, gain adjustments in amplifiers in radar systems were made using a delta gain control AGC circuit for multiple channels of the amplifier. However, even where each channel is separately adjusted, the relative gain among channels must not only be initially calibrated or equalized, but such equalization must be maintained over time as well. Therefore the prior practice has been to provide an additional delta gain control AGC circuit to compensate for drifts in gain among the various channels of a multiple channel amplifier. Nevertheless, such prior art designs require periodic checking to match the gain of the multiple channels.
In addition prior art circuits which incorporate some type of gain reduction inherently, by virtue of their design, affect the noise figure of the amplifier, namely the higher the gain reduction the higher the noise figure. Similarly, the gain of such prior art circuits may become non-linear at high gain reduction.
What is needed then is a design for an amplifier which includes an accurate gain control which is of such a design that:
(a) the need for periodic checking, particularly in a multiple channel amplifier is eliminated, and (b) the gain does not lose linearity or suffer a deterioration of its noise figure with higher gain reduction.